The present invention relates to an interlayer dielectric film with a low dielectric constant capable of preventing diffusion of copper, that is, a material for interconnects.
In an interlayer dielectric film of a VLSI, reduction of design rule has led to a problem of increase of parasitic capacitance between adjacent interconnects, and it is significant to lower the dielectric constant of the interlayer dielectric film in order to reduce the parasitic capacitance between interconnects.
As a low dielectric interlayer dielectric film, a siloxane film, such as a methylsilsesquioxane (MSQ) film (with a dielectric constant of approximately 2.9) and a hydrogenated silsesquioxane (HSQ) film (with a dielectric constant of approximately 3.0), including SiO2 as a principal constituent has been proposed. FIG. 14 shows the chemical structure of methylsilsesquioxane, that is, an example of conventional organic siloxane in which an organic group is bonded to siloxane. In FIG. 14, a methyl group is bonded to a Si atom included in the main chain of the siloxane.
Alternatively, an organic polymer film including an aromatic compound polymer, such as a polyimide derivative, a polyalyl ether derivative, a polyquinoline derivative or a polyparaxylene derivative, having a low dielectric constant and high heat resistance has been proposed as the low dielectric interlayer dielectric film. Such an organic polymer film has a low dielectric constant because it includes carbon as a principal constituent, and hence, the polarizability of molecules included in the film is lower than that of a conventionally used interlayer dielectric film including SiO2 as a principal constituent. Therefore, such an organic polymer film is regarded as a promising low dielectric interlayer dielectric film.
However, when copper is used as the material for interconnects, copper ions are diffused by an electric field or heat into such a low dielectric interlayer dielectric film. Therefore, the breakdown voltage of the interlayer dielectric film is disadvantageously lowered when it is used for a long period of time. When the breakdown voltage of the interlayer dielectric film is lowered, dielectric failure is caused, which may result in failure of the operation of the VLSI.